A seat belt device for restraining a vehicle occupant is equipped with a webbing retractor. Among webbing retractors, there are those provided with a tension reducer which is for mitigating or eliminating an excessive constricting sensation at the time the webbing is applied, or a pretensioner mechanism which, by taking-up a predetermined amount of a webbing onto a take-up shaft when the vehicle is in a state of rapid deceleration or the like, eliminates the slight looseness called “slack” or the like and increases the force restraining the body of the vehicle occupant by the webbing and holds the body of the vehicle occupant even more reliably. Further, a so-called motorized retractor of a structure which carries out the above-described respective functions by a motor is known (as examples, refer to Patent Document 1 and Patent Document 2).
In this type of motorized retractor, for example, not only can the functions of a tension reducer and a pretensioner be exhibited as described above, but assisting of the taking-up and the pulling-out of the webbing at usual times of application of the webbing and the like are also possible, which is extremely advantageous.
In particular, in recent years, a structure has been conceived of in which, in a motorized retractor as described above, the distance to another vehicle or an obstacle in front is detected by a forward monitoring device such as a distance sensor or the like, and when the distance to the vehicle or obstacle in front becomes less than a given value, a motor is operated, and the take-up shaft is rotated in the take-up direction by the rotational force of the motor. In such a motorized retractor, in order to prevent the rotation from the take-up shaft side from being transferred to the motor, a clutch is interposed between the output shaft of the motor and the take-up shaft, and only rotation from the motor output shaft side is transferred to the take-up shaft by the clutch.
In such a motorized retractor, there are demands for compactness and weight reduction, a reduction in the manufacturing cost, and the like. Compactness and weight reduction, an improvement in the assemblability, and the like are required also of the clutch as described above.    Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2001-130376    Patent Document 2: Japanese Patent Application Laid-Open (JP-A) No. 2001-347923